Materials for organic light emitting diode

ABSTRACT

Organometallic compounds comprising a phenylquinoline or phenylisoquinoline ligand having the quinoline or isoquinoline linked to the phenyl ring of the phenylquinoline or phenylisoquinoline, respectively, via two carbon atoms. These compounds also comprise a substituent other than hydrogen and deuterium on the quinoline, isoquinoline or linker. These compounds may be used as red emitters in phosphorescent OLEDs. In particular, these compounds may provide stable, narrow and efficient red emission.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 13/195,544, filed Aug. 1, 2011. This application is also a continuation-in-part (CIP) of U.S. application Ser. No. 12/044, 234, filed Mar. 7, 2008, which claims the benefit of U.S. Provisional Application No. 60/905,758, filed Mar. 8, 2007. Each of the aforementioned related patent applications is expressly incorporated herein by reference in its entirety.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, The University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs). More specifically, the present invention is related to organometallic compounds comprising a phenylquinoline or phenylisoquinoline ligand having the quinoline or isoquinoline linked to the phenyl ring of the phenylquinoline or phenylisoquinoline, respectively. The ligand also contains a bulky substituent on the quinoline, isoquinoline or two carbon atom linker. These compounds may be used in OLEDs to provide devices with improved lifetime and color. In particular, these compounds may be especially useful as stable, narrow and efficient red emissive compounds.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processable” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

Organometallic compounds comprising a phenylquinoline or phenylisoquinoline ligand having the quinoline or isoquinoline linked to the phenyl ring of the phenylquinoline or phenylisoquinoline, respectively, via a carbon linker are provided. The compounds also comprise a bulky substituent on the quinoline, isoquinoline, or linker. The compounds have the formula M(L₁)_(x)(L₂)_(y)(L₃)_(z).

The ligand L₁ is

The ligand L₂ is

The ligand L₃ is a third ligand.

Each L₁, L₂ and L₃ can be the same or different. M is a metal having an atomic number greater than 40. Preferably, M is Ir. x is 1, 2, or 3. y is 0, 1, or 2. z is 0, 1, or 2. x+y+z is the oxidation state of the metal M. R is a carbocyclic or heterocyclic ring fused to the pyridine ring. R is optionally further substituted with R′. A, B, and C are each independently a 5 or 6-membered carbocyclic or heterocyclic ring. R′, R_(Z), R_(A), R_(B), and R_(C) may represent mono, di, tri, or tetra substitutions. Each of R₁, R₂, R₃, R₄, R′, R_(Z), R_(A), R_(B), and R_(C) are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₁, R₂, R₃, R₄, and R′ is not hydrogen or deuterium. Any two adjacent R₁, R₂, R₃, R₄, and R′ are optionally linked to form an alkyl ring.

In one aspect, at least one of R₁, R₂, R₃, R₄, and R′ is an alkyl. In another aspect, R′ is not hydrogen or deuterium. Preferably, at least one of R₁, R₂, R₃, R₄, and R′ is an alkyl having more than 2 carbon atoms. More preferably, at least one of R₁, R₂, R₃, R₄, and R′ is isobutyl.

In one aspect, L₃ is a monoanionic bidentate ligand.

In another aspect, L₃ is

and R′₁, R′₂, and R′₃ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. Preferably, R′₂ is hydrogen. More preferably, at least one of R′₁, R′₂, and R′₃ contains a branched alkyl moiety with branching at a position further than the α position to the carbonyl group. Most preferably, at least one of R′₁ and R′₃ is isobutyl.

In one aspect, the compound has the formula:

R₅ and R₆ may represent mono, di, tri, or tetra substitutions. Each of R₅ and R₆ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₁, R₂, R₃, R₄, and R₆ is not hydrogen or deuterium. m is 1, 2, or 3.

in another aspect, the compound has the formula:

R₅ and R₆ may represent mono, di, tri, or tetra substitutions. Each of R₅ and R₆ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₁, R₂, R₃, R₄, and R₆ is not hydrogen or deuterium. m is 1, 2, or 3.

In one aspect, the compound is homoleptic. In another aspect, the compound is heteroleptic.

Specific non-limiting examples of organometallic compounds comprising a phenylquinoline or phenylisoquinoline ligand having the quinoline or isoquinoline linked to the phenyl ring of the phenylquinoline or phenylisoquinoline, respectively, are provided. These compounds also have a bulky substituent on the quinoline, isoquinoline, or linker. In one aspect, the compound is selected from the group consisting of:

Preferably, the compound is:

Additionally, a first device comprising a first organic light emitting device is provided. The organic light emitting device further comprises an anode, a cathode, and an organic layer, disposed between the anode and the cathode. The organic layer further comprises a compound having the formula M(L₁)_(x)(L₂)_(y)(L₃)_(z), as described above.

The ligand L₁ is

The ligand L₂ is

The ligand L₃ is a third ligand.

Each L₁, L₂ and L₃ can be the same or different. M is a metal having an atomic number greater than 40. x is 1, 2, or 3. y is 0, 1, or 2. z is 0, 1, or 2. x+y+z is the oxidation state of the metal M. R is a carbocyclic or heterocyclic ring fused to the pyridine. R is optionally further substituted with R′. A, B, and C are each independently a 5 or 6-membered carbocyclic or heterocyclic ring. R′, R_(Z), R_(A), R_(B), and R_(C) may represent mono, di, tri, or tetra substitutions. Each of R₁, R₂, R₃, R₄, R′, R_(Z), R_(A), R_(B), and R_(C) are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₁, R₂, R₃, R₄, and R′ is not hydrogen or deuterium. Any two adjacent R₁, R₂, R₃, R₄, and R′ are optionally linked to form an alkyl ring.

The various specific aspects discussed above for compounds having the formula M(L₁)_(x)(L₂)_(y)(L₃)_(z) are also applicable to a compound having M(L₁)_(x)(L₂)_(y)(L₃)_(z) that is used in the first device. In particular, specific aspects of L₁, L₂, L₃, A, B, C, R_(A), R_(B), R_(C), R_(Z), R, R′, R₁, R₂, R₃, R₄, R₅, R₆, R′₁, R′₂, R′₃, M, m Formula III and Formula IV of the compound having the formula M(L₁)_(x)(L₂)_(y)(L₃)_(z) are also applicable to a compound having M(L₁)_(x)(L₂)_(y)(L₃)_(z) that is used in the first device.

In one aspect, the first device is a consumer product. In another aspect, the first device is an organic light emitting device. In yet another aspect, the first device comprises a lighting panel.

In one aspect, the organic layer is an emissive layer and the compound is an emissive dopant. In another aspect, the organic layer further comprises a host. Preferably, the host is a metal 8-hydroxyquinolate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIG. 3 shows a phenylquinoline or phenylisoquinoline ligand with the quinoline or isoquinoline linked to the phenyl ring of the phenylquinoline or phenylisoquinoline, respectively, and comprising a bulky substituent.

FIG. 4 shows exemplary organometallic compounds comprising phenylquinoline or phenylisoquinoline ligand with the quinoline or isoquinoline linked to the phenyl ring of the phenylquinoline or phenylisoquinoline, respectively, and comprising a bulky substituent.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, and a cathode 160. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. patent application Ser. No. 10/233,470, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processability than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl, heterocyclic group, aryl, aromatic group, and heteroaryl are known to the art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32, which are incorporated herein by reference.

A novel class of organometallic compounds is provided. The compounds comprise a phenylquinoline or phenylisoquinoline ligand having the quinoline or isoquinoline linked to the phenyl ring of the phenylquinoline or phenylisoquinoline, respectively, via two carbon atoms, e.g., a linked phenylquinoline or linked phenylisoquinoline (as illustrated in FIG. 3). In addition, the ligand also includes at least one substituent other than hydrogen and deuterium on the quinoline, isoquinoline or two carbon atoms linking the quinoline or isoquinoline to the aromatic ring, i.e., bulky substituent. These compounds may be used as red emitters in phosphorescent OLEDs. In particular, these compounds may provide stable, narrow and efficient red emission as a result of the rigidification and addition of a bulky substituent.

The compounds disclosed herein may provide narrow red emission as a result of rigidification, which may narrow the EL spectrum. The spectrum at half maximum (FWHW) of an organic molecule may narrow as the molecules become more rigid. The compounds disclosed herein are made more rigid by linking the top portion of the ligand, e.g., a quinoline or isoquinoline, to the bottom portion of the ligand, e.g., phenyl ring. For example, the compounds may include a linked phenylquinoline or linked phenylisoquinoline. In particular, a compound comprising a 2-phenylquinoline ligand in which the quinoline has been linked to the phenyl ring may have a narrower EL spectrum. A narrow EL spectrum is a desirable property of electroluminescent materials for use in an OLED.

As discussed above, a two carbon atom linker links the quinoline or isoquinoline to the phenyl ring of the phenylquinoline or phenylisoquinoline. Without being bound by theory, it is believed that using only carbon atoms as linkers may provide better device stability, i.e., longer device lifetime, when compared to other linkers, such as those with oxygen atoms. Additionally, it is believed that two atoms in the linker backbone, rather than one atom, is desirable. One atom linker may be too small, resulting in an increased coordinating binding angle of the ligand to metal on the other side of the ligand, which may reduce the bond strength of metal to ligand, and, in turn, decrease the stability of the metal complex.

Moreover, the compounds disclosed herein may provide stable and efficient red emission as a result of having a substituent other than hydrogen and deuterium on the quinoline, isoquinoline or two carbon atoms in the linked ligand. Without being bound by theory, it is believed that the addition of a bulky substituent to the linked ligand may prevent aggregation and self quenching in the compound, thereby providing higher device efficiency.

Without being bound by theory, it may be particularly advantageous to have an alkyl substituent as the bulky group on the linked ligand because alkyls offer a wide range of tunability. In particular, an alkyl substituent may be useful for tuning the evaporation temperature, solubility, energy levels, device efficiency and narrowness of the emission spectrum of the compound. Additionally, alkyl groups can be stable functional groups chemically and in device operation. For example, a linked ligand comprising an alkyl substituent on the quinoline may provide increased efficiency.

Organometallic compounds comprising a phenylquinoline or phenylisoquinoline ligand containing a quinoline or isoquinoline linked to the phenyl ring of the phenylquinoline or phenylisoquinoline, respectively, via two carbon atoms are provided (as illustrated in FIG. 4). The compounds also comprise a bulky substituent, i.e., not hydrogen or deuterium, on the quinoline, isoquinoline, or linker. The compounds have the formula M(L₁)_(x)(L₂)_(y)(L₃)_(z).

The ligand L₁ is

The ligand L₂ is

The ligand L₃ is a third ligand.

Each L₁, L₂ and L₃ can be the same or different. M is a metal having an atomic number greater than 40. Preferably, M is Ir. x is 1, 2, or 3. y is 0, 1, or 2. z is 0, 1, or 2. x+y+z is the oxidation state of the metal M. R is a carbocyclic or heterocyclic ring fused to the pyridine. R is optionally further substituted with R′. A, B, and C are each independently a 5 or 6-membered carbocyclic or heterocyclic ring. R′, R_(Z), R_(A), R_(B), and R_(C) may represent mono, di, tri, or tetra substitutions. Each of R₁, R₂, R₃, R₄, R′, R_(Z), R_(A), R_(B), and R_(C) are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₁, R₂, R₃, R₄, and R′ is not hydrogen or deuterium. Any two adjacent R₁, R₂, R₃, R₄, and R′ are optionally linked to form an alkyl ring.

For the compounds disclosed herein, a bulky substituent is present on the quinoline, isoquinoline or two carbon atoms in the linked ligand. The bulky group may be a halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, i.e., bulky group is a substituent other than hydrogen or deuterium. Without being bound by theory, it is believed that the bulky substituent is least likely to affect the emission color of the compound If it is placed at one or more of the R₁, R₂, R₃, R₄, and R′ positions.

In one aspect, at least one of R₁, R₂, R₃, R₄, and R′ is an alkyl. In another aspect, R′ is not hydrogen or deuterium. Preferably, at least one of R₁, R₂, R₃, R₄, and R′ is an alkyl having more than 2 carbon atoms. More preferably, at least one of R₁, R₂, R₃, R₄, and R′ is isobutyl.

In one aspect, L₃ is a monoanionic bidentate ligand.

In another aspect, L₃ is

and R′₁, R′₂, and R′₃ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. Preferably, R′₂ is hydrogen. More preferably, at least one of R′₁, R′₂, and R′₃ contains a branched alkyl moiety with branching at a position further than the α position to the carbonyl group. Most preferably, at least one of R′₁ and R′₃ is isobutyl.

In one aspect, the compound has the formula:

R₅ and R₆ may represent mono, di, tri, or tetra substitutions. Each of R₅ and R₆ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₁, R₂, R₃, R₄, and R₆ is not hydrogen or deuterium. m is 1, 2, or 3.

In another aspect, the compound has the formula:

R₅ and R₆ may represent mono, di, tri, or tetra substitutions. Each of R₅ and R₆ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₁, R₂, R₃, R₄, and R₆ is not hydrogen or deuterium. m is 1, 2, or 3.

Generally, it is desirable to maintain red emission while improving other properties of these compounds, such as evaporation temperature and solubility. In some instances, it may be desirable for the compound to have a less bulky substituent on ring A. Ring A, e.g., benzene, may be substituted with hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, as discussed above. However, it is thought that placing a bulky substituent on ring A may cause a pronounced shift in the emission color of the compound. In some aspects, then, it is preferable to substitute ring A with less bulky chemical substituents to maintain good red emission while improving other properties of the compound, such as evaporation temperature and solubility.

In one aspect, the compound is homoleptic. In another aspect, the compound is heteroleptic.

Specific non-limiting examples of organometallic compounds comprising a phenylquinoline or phenylisoquinoline ligand having the quinoline or isoquinoline linked to the phenyl of the phenylquinoline or phenylisoquinoline, respectively, via a 2 carbon atom linker are provided. These compounds also comprise a bulky substituent on the quinoline, isoquinoline, or linker. In one aspect, the compound is selected from the group consisting of:

Preferably, the compound is:

Additionally, a first device comprising a first organic light emitting device is provided. The organic light emitting device further comprises an anode, a cathode, and an organic layer, disposed between the anode and the cathode. The organic layer further comprises a compound having the formula M(L₁)_(x)(L₂)_(y)(L₃)_(z).

The ligand L₁ is

The ligand L₂ is

The ligand L₃ is a third ligand.

Each L₁, L₂ and L₃ can be the same or different. M is a metal having an atomic number greater than 40. x is 1, 2, or 3. y is 0, 1, or 2. z is 0, 1, or 2. x+y+z is the oxidation state of the metal M. R is a carbocyclic or heterocyclic ring fused to the pyridine ring. R is optionally further substituted with R′. A, B, and C are each independently a 5 or 6-membered carbocyclic or heterocyclic ring. R′, R_(Z), R_(A), R_(B), and R_(C) may represent mono, di, tri, or tetra substitutions. Each of R₁, R₂, R₃, R₄, R′, R_(Z), R_(A), R_(B), and R_(C) are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₁, R₂, R₃, R₄, and R′ is not hydrogen or deuterium. Any two adjacent R₁, R₂, R₃, R₄, and R′ are optionally linked to form an alkyl ring.

The various specific aspects discussed above for compounds having the formula M(L₁)_(x)(L₂)_(y)(L₃)_(z) are also applicable to a compound having M(L₁)_(x)(L₂)_(y)(L₃), that is used in the first device. In particular, specific aspects of L₁, L₂, L₃, A, B, C, R_(A), R_(B), R_(C), R_(Z), R, R′, R₁, R₂, R₃, R₄, R₅, R₆, R′₁, R′₂, R′₃, M, m Formula III and Formula IV of the compound having the formula M(L₁)_(x)(L₂)_(y)(L₃)_(z), are also applicable to a compound having M(L₁)_(x)(L₂)_(y)(L₃)_(z) that is used in the first device.

In one aspect, the first device is a consumer product. In another aspect, the first device is an organic light emitting device. In yet another aspect, the first device comprises a lighting panel.

In one aspect, the organic layer is an emissive layer and the compound is an emissive dopant. In another aspect, the organic layer further comprises a host. Preferably, the host is a metal 8-hydroxyquinolate.

Combination with Other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but not limit to: a phthalocyanine or porphryin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and silane derivatives; a metal oxide derivative, such as MoO_(x); a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, but not limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each Ar is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the group consisting of:

k is an integer from 1 to 20; X¹ to X⁸ is C (including CH) or N; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit to the following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹-Y²) is a bidentate ligand, Y¹ and Y² are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹-Y²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹-Y²) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant.

Examples of metal complexes used as host are preferred to have the following general formula:

M is a metal; (Y³-Y⁴) is a bidentate ligand, Y³ and Y⁴ are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y³-Y⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, host compound contains at least one of the following groups in the molecule:

R¹ to R⁷ is independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from C (including CH) or N.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED.

In one aspect, compound used in HBL contains the same molecule used as host described above.

In another aspect, compound used in HBL contains at least one of the following groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons.

In one aspect, compound used in ETL contains at least one of the following groups in the molecule:

R¹ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but not limit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exiton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in Table 1 below. Table 1 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

TABLE 1 MATERIAL EXAMPLES OF MATERIAL PUBLICATIONS Hole injection materials Phthalocyanine and porphryin compounds

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J. Lumin. 72-74, 985 (1997) CF_(x) Fluorohydrocarbon polymer

Appl. Phys. Lett. 78, 673 (2001) Conducting polymers (e.g., PEDOT:PSS, polyaniline, polypthiophene)

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US20030162053 Triarylamine or polythiophene polymers with conductivity dopants

EP1725079A1

Arylamines complexed with metal oxides such as molybdenum and tungsten oxides

SID Symposium Digest, 37, 923 (2006) WO2009018009 p-type semiconducting organic complexes

US20020158242 Metal organometallic complexes

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U.S. Pat. No. 5,061,569

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Adv. Mater. 6, 677 (1994), US20080124572 Triarylamine with (di)benzothiophene/ (di)benzofuran

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Synth. Met. 111, 421 (2000) Isoindole compounds

Chem. Mater. 15, 3148 (2003) Metal carbene complexes

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Nature 395, 151 (1998)

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WO2009066779, WO2009066778, WO2009063833, US20090045731, US20090045730, WO2009008311, US20090008605, US20090009065 Zinc complexes

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Appl. Phys. Lett. 78, 1622 (2001)

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WO2004093207 Metal phenoxybenzooxazole compounds

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J. Appl. Phys. 90, 5048 (2001)

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Appl. Phys. Lett, 82, 2422 (2003)

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WO2006114966, US20090167162

US20090167162

WO2009086028

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WO2009003898 Silicon/Germanium aryl compounds

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WO2006100298 High triplet metal organometallic complex

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Nature 395, 151 (1998) Iridium (III) organometallic complexes

Appl. Phys. Lett. 78, 1622 (2001)

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US20070087321

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WO2009100991

WO2008101842 Platinum (II) organometallic complexes

WO2003040257 Osminum (III) complexes

Chem. Mater. 17, 3532 (2005) Ruthenium (II) complexes

Adv. Mater. 17, 1059 (2005) Rhenium (I), (II), and (III) complexes

US20050244673 Green dopants Iridium (III) organometallic complexes

Inorg. Chem. 40, 1704 (2001) and its derivatives

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U.S. Pat. No. 7,332,232

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US20070190359

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US20090165846

US20080015355 Monomer for polymeric metal organometallic compounds

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Appl. Phys. Lett. 86, 153505 (2005)

Appl. Phys. Lett. 86, 153505 (2005)

Chem. Lett. 34, 592 (2005)

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WO2009000673 Gold complexes

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US20030138657 Organometallic complexes with two or more metal centers

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Appl. Phys. Lett. 75, 4 (1999)

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Appl. Phys. Lett. 81, 162 (2002) 5-member ring electron deficient heterocycles such as triazole, oxadiazole, imidazole, benzoimidazole

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EXPERIMENTAL Compound Examples Example 1 Synthesis of Compound 9

Synthesis of (2-amino-6-chlorophenyl)methanol

2-Amino-6-chlorobenzoic acid (25.0 g, 143 mmol) was dissolved in 120 mL of anhydrous THF in a 500 mL 2 neck round bottom flask. The solution was cooled in an ice-water bath. 215 mL of 1.0 M lithium aluminum hydride (LAH) THF solution was then added dropwise. After all of the LAH was added, the reaction mixture was allowed to warm up to room temperature and stirred at room temperature for overnight. ˜10 mL of water was added to the reaction mixture followed by 7 g 15% NaOH. An additional 20 g of water was added to the reaction mixture. Decant the organic THF phase and the solid was added with ethyl acetate. ˜200 mL and stirring and combined ethyl acetate organic portion and THF portion and added Na₂SO₄ drying agent. The mixture was filtered and evaporated. ˜20 g yellow solid was obtained without further purification for next step reaction.

Synthesis of 8-chloro-2,4-dimethyl-5,6-dihydrobenzo[c]acridine

(2-Amino-6-chlorophenyl)methanol (16 g, 101 mmol), 5,7-dimethyl-3,4-dihydronaphthalen-1(2H)-one (20.0 g, 111 mmol), RuCl₂(PPh₃)₃ (0.971 g, 1.01 mmol), and KOH (5.7 g, 101 mmol) were refluxed in 200 mL of toluene for 12 h. Water was collected from the reaction using a Dean-stark trap. The reaction mixture was allowed to cool to room temperature and filtered through a silica gel plug and eluted with dichloromethane. The product was washed by methanol and recrystallized from hexane to obtain ˜20 gram of the desired product which was confirmed by GC-MS.

Synthesis of 8-isobutyl-2,4-dimethyl-5,6-dihydrobenzo[c]acridine

8-chloro-2,4-dimethyl-5,6-dihydrobenzo[c]acridine (15.0 g, 51.1 mmol), isobutylboronic acid (7.8 g, 77 mmol), dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (1.6 g, 4.08 mmol) potassium phosphate monohydrate (41.2 g, 179 mmol) were mixed in 300 mL of toluene. The system was degassed for 20 minutes. Pd₂(dba)₃ (0.93 g, 1.02 mmol) was then added and the system was refluxed overnight. After cooling to room temperature, the reaction mixture was filtered through a Celite® plug and eluted with 30% ethyl acetate in toluene. ˜19.5 crude liquid was obtained. The crude product was recrystallized from 5% acetone in hexane to obtain ˜14.9 g pure product (99.6%) which was confirmed by GC-MS.

Synthesis of iridium dimer

A mixture of 8-isobutyl-2,4-dimethyl-5,6-dihydrobenzo[c]acridine (11.5 g, 36.5 mmol), IrCl₃.4H₂O (4.5 g, 12.2 mmol), 2-ethoxyethanol (90 mL) and water (30 mL) was refluxed under nitrogen overnight. The reaction mixture was filtered and washed with MeOH (3×20 mL) ˜9 g of dimer was obtained after vacuum drying. The dimer was used for the next step without further purification.

Synthesis of Compound 9

Dimer (3.5 g, 2.07 mmol), pentane-2,4-dione (2.07 g, 20.7 mmol), Na₂CO₃ (2.19 g, 20.7 mmol) and 2-ethoxyethanol (100 mL) were stirred at room temperature for 24 h. The precipitate was filtered and washed with methanol. The solid was further purified by passing it through a silica gel plug (that was pretreated with 15% TEA in hexanes) and eluted with methylene chloride. 0.6 g of product Compound 9 was obtained after purification. The compound was confirmed by LC-MS.

Example 2 Synthesis of Compound 10

Compound 10 was synthesized in same way as Compound 9, and confirmed by LC-MS.

Device Examples

All example devices were fabricated by high vacuum (<10⁻⁷ Torr) thermal evaporation. The anode electrode is 1200 Å of indium tin oxide (ITO). The cathode consisted of 10 Å of LiF followed by 1,000 Å of Al. All devices are encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H₂O and O₂) immediately after fabrication, and a moisture getter was incorporated inside the package.

The organic stack of the Device Examples consisted of sequentially, from the ITO surface, 100 Å of Compound A as the hole injection layer (HIL), 300 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the hole transporting layer (HTL), 300 Å of the invention compound doped in BAlq as host with 4, 6 or 8 wt % of an Ir phosphorescent compound as the emissive layer (EML), 500 or 550 Å of Alq₃ (tris-8-hydroxyquinoline aluminum) as the ETL.

Comparative Device Examples with Compound B was fabricated similarly to the Device Examples, except that Compound B is used as the emitter in the EML.

As used herein, Compound A, Compound B and other compounds used in the device examples have the following structures:

The device structures are summarized in Table 2, and the device data is summarized in Table 3. Cmpd. is an abbreviation of Compound. Ex. is an abbreviation of Example. Comp. Ex. is an abbreviation of Comparative Example.

TABLE 2 Example HIL HTL EML (doping %) ETL Ex. 1 Compound A NPD Balq Compound 10 Alq 7% Ex. 2 Compound A NPD Balq Compound 9 Alq 8% Comp. Ex. 1 Compound A NPD Balq Compound B Alq 8%

TABLE 3 At 1000 nits At 2000 nits λ_(max) FWHM Voltage LE EQE PE LT_(97%) Cmpd. x y [nm] [nm] [V] [cd/A] [%] [lm/W] [Hr] Ex. 1 0.649 0.348 612 54 8.9 12.5 10.1 4.4 29.9 Ex. 2 0.656 0.341 616 62 8.8 8.5 8.0 3.0 8.5 Comp. 0.651 0.346 612 60 9.7 9.9 8.6 3.2 9.5 Ex. 1

Table 3 is a summary of the device data. The luminous efficiency (LE), external quantum efficiency (EQE) and power efficiency (PE) were measured at 1000 nits, while the lifetime (LT_(97%)) was defined as the time required for the device to decay to 97% of its initial luminance at 2000 nits under a constant current density.

As seen from Table 3, the EQE measured at 1000 nits for a device comprising Compound 10 is 17% higher than the EQE measured for a device comprising Compound B. Additionally, the EL spectral full width at half maximum (FWHW) of Compound 10 is also narrower than the FWHM of Compound B, i.e, FWHM of Compound 10 is 54 nm, while the FWHM of Compound B is 60 nm. The FWHM of Compound 9, however, is similar to the FWHM of Compound B. It is a desirable device property to have a narrow FWHM. These results indicate that Compound 10 is a more efficient red emitter than Compounds B with a desirable narrower FWHM.

Compound 10 also has a longer lifetime than Compound B, i.e., the LT_(97%) measured at room temperature for Compound 10 is about three times as long as the LT_(97%) measured at room temperature for Compound B. Compound 10 differs from Compound B in that it has a bulkier substituent on quinoline ring. Therefore, devices comprising a compound with a substituent on the quinoline ring may have significantly improved performance.

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

1-24. (canceled)
 25. A compound of formula III

wherein each of R₁, R₂, R₃, R₄, R₅, R₆, R₁′, R₂′, and R₃′ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein at least one R₆ comprises more than 2 carbon atoms; wherein any two adjacent R₁, R₂, R₃, and R₄ are optionally linked to form an alkyl ring; wherein R₅ may represent mono, di or tri substitutions; wherein R₆ may represent mono, di, tri, or tetra substitutions; and wherein m is 1 or
 2. 26. The compound of claim 25, wherein at least one of R₁, R₂, R₃ and R₄ is an alkyl.
 27. The compound of claim 25, wherein at least one of R₁, R₂, R₃ and R₄, is an alkyl having more than 2 carbon atoms.
 28. The compound of claim 25, wherein at least one of R₁, R₂, R₃, R₄, and R₆ is isobutyl.
 29. The compound of claim 25, wherein at least one of R′₁, R′₂, and R′₃ contains a branched alkyl moiety with branching at a position further than the α position to the carbonyl group.
 30. The compound of claim 25, wherein at least one of R′₁ and R′₃ is isobutyl.
 31. The compound of claim 25, wherein R′₂ is hydrogen.
 32. The compound of claim 25, wherein R₆ is selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, arylakyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, and heteroaaryl.
 33. The compound of claim 25, wherein the compound is selected from the group consisting of:


34. The compound of claim 25, wherein the compound is selected from the group consisting of:


35. A first device comprising a first organic light emitting device, further comprising: an anode; a cathode; and an organic layer, disposed between the anode and the cathode, comprising a compound of Formula III:

wherein each of R₁, R₂, R₃, R₄, R₅, R₆, R₁′, R₂′, and R₃′ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein at least one R₆ comprises more than 2 carbon atoms; wherein any two adjacent R₁, R₂, R₃, and R₄ are optionally linked to form an alkyl ring; wherein R₅ may represent mono, di or tri substitutions; wherein R₆ may represent mono, di, tri, or tetra substitutions; and wherein m is 1 or
 2. 36. The first device of claim 35, wherein the first device is a consumer product.
 37. The first device of claim 35, wherein the first device is an organic light emitting device.
 38. The first device of claim 35, wherein the first device comprises a lighting panel.
 39. The first device of claim 35, wherein the organic layer is an emissive layer and the compound is an emissive dopant.
 40. The first device of claim 35, wherein the organic layer further comprises a host.
 41. The first device of claim 35, wherein the host is a metal 8-hydroxyquinolate. 